Generally, a service capability exposure function (SCEF) is requested by a server, such as a service capability server (SCS) or an application server (AS), to add a device or user equipment (UE) to the multicast group. While the device or UE may be in contact with a mobile network operator, an application on the device does not know it is a member of a multicast group. To accommodate this, two approaches typically are employed. In one approach, a server may unicast a message to each device informing it of the multicast group. The unicast message may carry details of the multimedia broadcast multicast service (MBMS). In another approach, the device may contact the SCEF over the user plane to learn details on the group including, for example, the multi-cast address and temporary mobile group identity (TMGI). However, the device does not know when it should contact the SCEF and query for this information.
Complications nevertheless exist with the two approaches stated above. For instance, when the SCS/AS requests the SCEF to add a member to the group, the SCEF presumes that the device has joined the group. This may not be accurate especially if the device's policies and capabilities do not match with those required by the server. This may occur in instances when the device decides not to join the group or delay joining the group. Separately, while the device may have joined the group, it may still not be activated. That is, the device is not listening to multicast messages from the server.
The approaches discussed above require the server to see the underlying transport details of the MBMS to the device. Specifically, the device assumes that that the SCS/AS knows about the specific details of the MBMS device context, e.g., Multicast Address, TMGI, etc. Meanwhile, the SCS/AS assumes there is an application on the device that listens for the unicast message from the SCS/AS to join the MBMS group. The transport details stray from the desired objective of hiding the underlying group delivery and transport details from the server.